WO1994006871A1

WO1994006871A1 - A sign, a method of making the sign and an ink therefor

Info

Publication number: WO1994006871A1
Application number: PCT/GB1993/001936
Authority: WO
Inventors: Morton Graham
Original assignee: Canterbury Park Limited
Priority date: 1992-09-17
Filing date: 1993-09-13
Publication date: 1994-03-31
Also published as: GB9219671D0; AU4979393A

Abstract

There are disclosed an ink, particularly for an edge lit sign, an edge lit sign and a method of making an edge lit sign. The sign has a sheet or substrate (14) of transparent material along which light is transmitted from a light box (18). One side of the sheet is printed with an ink (23) of the invention which has been diluted, as by a carrier to maintain pigment particles (25) in suspension whilst separating them to provide more clear matrix (26) through which illuminating light can pass and allowing more light to be reflected and pass down the substrate (24). The sheet can be engraved to direct more light into the pigment.

Description

A Sign, A Method of Making the Sign and an Ink Therefor.

This invention relates to signs, particularly edge-lit signs and to inks therefor.

An edge lit sign consists of a sheet of transparent, usually colourless material such as glass or plastics. The most popular plastics material in use is transparent acrylic material although polycarbonate can be used. The latter material is, however, rather more expensive than acrylic and it can be difficult to obtain inks compatible with polycarbonate sheets. In view of this and the ease with which acrylic sheet can be cut and formed compared with glass makes acrylic sheet by far the favourite material for such signs.

An edge-lit sign is illuminated by a light box along one edge of the sheet and the light is internally reflected along the sheet and impinges upon and illuminates ink on one surface of the sheet. In the case of a sign without alphanumeric characters (that is to say a purely pictorial sign) the printed material is equally visible from both sides of the sign. For alphanumeric characters the sign is only operative from one side. The benefit of edge lit signs is that they are relatively thin so that they can be placed against walls and do not have to have a large light box behind them which would be necessary with a sign which is lit from its rear by a lamp and a condenser or diffuser. (NOTE: I am correct here? Is it possible to make a single sheet two-way sign?)

One of the problems with some signs of this type is the fact that when more than a small area of printing is provided that part of the ink layer which is nearer the light box is more strongly illuminated, and therefore shows up as a brighter surface, than the rest of the printing further away from the light box. In many typical signs, varying in size from 200mm up to 1 m, it is usually possible only to get a bright illumination over about the first 20 or 30% of the printing, the rest of the printing being darker. This is a severe disadvantage with edge lit signs. It tends to restrict their only effective use to relatively small signs lit by a lamp box along a longer edge where the illumination can be tolerated.

Figures 1, 2, 3 and 5a illustrate the problem which is inherent in conventional ink. Inks used for printing this type of sign are translucent inks, which are arranged so that when light enters from one side of the layer, light issuing from the other side is of a desired colour dependent on the colour of the pigment particles embedded within the ink. Figure 1 shows a layer of ink as manufactured and also after having been placed on a surface (not shown) and allowed to dry. The layer (10) comprises a transparent matrix (11) throughout which are uniformly and closely dispersed individual pigment particles (12) . The matrix (11) is, when the ink is supplied, a non-polymerised plastics material. In the case of an acrylic ink this would be acrylate based forming a polyacrylate on drying. During the conventional screen printing process the ink is usually diluted with thinners which, in the case of the acrylic ink may be 2 butoxy ethyl acetate. This produces more fluid ink which can be handled easily and printed easily. Figure 2 shows a layer of ink containing thinners lying on a substrate (14) . It will be seen that the pigment particles (15) are well separated by the dilute matrix (16) . During drying the thinners evaporates and the thickness of the matrix (11)falls to the same thickness as that shown in figure 1 containing the basic matrix (11) and the pigment particles (12) . As screen printing is invariably carried out with the substrate (14) horizontal, it will be seen, from figure 3, that there is a tendency (exaggerated for clarity here) for pigment particles (15) to fall towards the substrate (14) .

This has two effects on the performance of the ink in this particular circumstance. Firstly, (see figure 5a) light (17) travelling down the substrate (14) from light box (18) usually an elongate extrusion or like housing with a fluorescent tube or similar elongate light source will usually be travelling at a relatively shallow angle by the time it reaches the ink layer

(19) . When it contacts the interface (20) between ink (19) and substrate (14) it will either contact a pigment particle (15) or it will contact the interface. The light which contacts a pigment particle will be reflected back into the substrate (14) as coloured light, the remainder of the spectral range being absorbed by the pigment. Light which touches the interface where there is no pigment will be partially reflected back into the substrate (14) as white light (assuming white light is issuing from the light box (18)) and will partially enter into the transparent matrix (16) . The light which passes the interface (20) and enters into the matrix (16) gives the ink layer (19) its illuminated effect. A typical such ray is shown at (21) and it will be seen that when it has passed the interface

(20) it has been reflected once or more times between particles of pigment and is therefore of the colour of the pigment and then issues from the front surface (22) of the ink layer (19) .

In the prior art ink layer shown in figure 3 and figure 5 there is quite a dense layer of pigment particles adjacent the interface which has two deleterious effects. Firstly, because the particles are relatively close together in the direction of the surface of the substrate (14) only a relatively small percentage of light travels towards the interface (20) will hit the interface between substrate and matrix (16) and be reflected as white light back into the substrate. This means that as the light travelled along the substrate (14) its intensity diminishes quite rapidly (see figure 7a) .

The further disadvantage is that the relatively thin layer of pigment adjacent the interface (20) mean that as a majority of light is reflected, less light can enter into the body of the matrix and be reflected by the pigment to issue from the front surface (22) as coloured light. There is also the further minor effect that any light which hits the front surface (22) and is reflected back into the matrix (16) will almost certainly be contact or be absorbed by the closely packed pigment particles before it has a chance to re-enter the matrix (14) and be useful again.

It can be seen that attempts by users of the prior known ink and methods to reduce the thickness of the layer by using less ink have been unsuccessful. Once the ink has been reduced sufficiently in thickness to allow the light to pass through, so much light passes through without multiple reflection between pigment particles that much of it is white light and therefore the pigment appears very pale indeed.

It is an object of the present invention to provide an improved ink for use, for example, in edge lit signs, an improved edge lit sign and an improved method of making an edge lit sign.

The invention provides an ink, for example for an edge lit sign wherein the pigment concentration is reduced below the conventional level. The concentration of the pigment is desirably reduced by addition of a carrier.

The carrier can be the same type of carrier used in the conventional ink.

The carrier can be a carrier conventionally used for supporting particles, for example, metallic particles in suspension in the ink.

The action of the dilution of the carrier is desirably such as to reduce the concentration of pigment particles within a given volume of ink whilst maintaining their uniform separation throughout the ink during application and drying of the ink.

The dilution of the conventional basic ink can be by addition of 1 to 20 parts by volume of the carrier per part of ink.

It can be advantageous to vary the dilution depending upon the colour of the ink, lighter inks being diluted with less carrier and darker inks being diluted more carrier. For example, one part of a yellow or white ink may be diluted 1 to 1 with carrier, whereas a dark green or dark blue ink may be diluted from 1 to 10 to 1 to 15 with carrier parts by volume.

It is possible to add a certain amount of thinners to the diluted ink in order to give it a more fluid consistency for handling and pouring onto the printing apparatus. However, it is desirable that use of thinners is kept to a minimum in order to avoid the problem of pigment sinking as discussed earlier.

The invention also provides a method of making an edge lit sign including providing a sheet of transparent material, providing a light box at one edge of that material and, printing on one side of the sheet using an ink aforesaid.

Desirably the degree of dilution of the ink is chosen such that the intensity of the observed ink from the direction away from the light box is significantly reduced compared with conventional edge lit signs.

Desirably the reduction intensity from the edge of the ink body adjacent the light box to its opposite side is less than 50%.

Desirably it is less than 25%.

Advantageously a reflecting surface is provided on an edge of the sheet remote from the light box. The reflected surface can be provided on the or all edges of the sheet remote from the light box.

The surface can be mirror reflective.

Desirably the surface is a diffuse reflective surface.

Desirably the surface is white.

The invention includes an edge lit sign made by the method aforesaid.

The invention also provides a method as aforesaid wherein the sheet is engraved. The engraving can be carried out in register with an edge of a printed area or can be carried out within a printed area.

It is further desirable if the depth of the engraving into the surface of the substrate is graduated so as to be shallower at a position adjacent the light box and deeper at a position remote from the light box.

The graduation can be a continuously variable graduation or can be carried out in steps. As well as being effected adjacent an ink area to enhance the reflection of light into the ink engraving can be carried out remote from or in register but distance from the ink so as to enhance the appearance of the sign in general.

The invention also provides an edge illuminated sign comprising a sheet of transparent material and a light box on an edge thereof, a surface of the sheet having been printed with a diluted ink.

Preferably the ink has been diluted with a carrier to maintain the pigment particles dispersed throughout the body of the ink.

Desirably the ink has been diluted sufficiently to ensure that the reduction and intensity across the area in a direction away from the light box is less than 50% from one side to the other.

Desirably the reduction is less than 25%.

The sheet can be engraved.

Desirably the engraving can be in register with an edge of an area of ink. Alternatively the engraving can be uniformally spaced from the ink or can be independent thereof.

The depth of engraving on the sheet can vary in depth being shallow adjacent the light box and deeper remote from the light box.

The graduation can be in steps or can be smoothly graduated.

Desirably the degree of dilution and suspension is such that considered in a direction away from the light box a given length of pigment layer will absorb a percentage of incident light not significantly greater than its own length is a percentage of the full length of the pigment area.

The invention will be described further, by way of example, with reference to the accompanying drawings wherein;

Figure 1 is a cross sectional view illustrating a film of conventional ink before or after drying;

Figure 2 shows the ink of figure l after dilution by thinners and coating onto a substrate;

Figure 3 shows the structure of figure 2 after evaporation of the thinners during drying of the ink.

Figure 4 is a view similar to figure 3 but showing ink of the invention on a substrate; Figures 5a and 5b illustrate an edge lit sign;

Figure 6 is a view similar to figure 5 but showing further features of a sign of the invention;

Figure 7a shows a schematic view of a conventional sign and its associated intensity graph; and

Figure 7b is an intensity graph of a sign of the invention.

Figures 1 to 3 and figure 5a have already been discussed in relation to the prior art and will not be discussed further here.

Referring to figures 4 and 5b, however, it will be seen that in an ink (23) of the invention coated onto a substrate (24) of a preferred sign of the invention, pigment particles (25) are relatively uniformly distributed throughout a transparent matrix (26) formed by polymerisation of the carrier to form an polyacrylate. (Query? Does an acrylate sheet actually consist of polyacrylate or am I getting my chemistry wrong?)

As best seen in figure 5b light contacting the interface (27) has, because of the greater longitudinal spacing of the pigment particles (25) a much greater chance of contacting a part of the interface (26) which is directly between the substrate (24) and the matrix (26) . Therefore, it has a much better chance of being reflected back into the substrate (24) rather than contacting a pigment particle and being significantly absorbed. This means that a much greater percentage of the light on a particular area of the ink layer can be reflected onwards down the substrate and can be reflected again from the rear surface of the sheet and perform its illuminating function in a direction further away from the light box (18) . Further, because there is more space between the pigment particles adjacent the interface (27) , there is much more possibility for light which does pass through the interface to reach the outer surface (28) of the ink layer (23) and pass therefrom. In a similar way, any light which hits the front surface (28) and is reflected backwards is not merely absorbed or reflected by the pigment but may also pass back through the matrix (26) and into the substrate (24) to continue down the substrate.

It might be thought that this extra transmissivity of the ink surface could cause a change in the perceived colour of the ink. This is true to a certain extent, because in practice a selection of the dilution and particular colour is made to give a desired colour of illumination. However, because the amount of thinners used is kept to a minimum, the mixture of basic ink and added carrier tends to be rather more viscous than ink diluted solely with thinners. This can result in a thicker layer of ink being deposited. Thus, it can be possible by using a given amount of ink to deposit, over a particular area, exactly the same quantity of pigment, but dispersed in a greater thickness of carrier giving, after drying a greater inter-particle separation as illustrated in figure 4.

This gives the desired multiple particle reflections for light passing from the substrate to the outer surface but also gives the necessary reflectivity at the interface (27) to cause a significant proportion of incident light to be reflected on down the substrate. Further, the keeping of the same quantity of pigment particles over a particular area the same as would happen in the conventional layer shown in figure 1 has the effect that light passing through the pigment will be coloured to an equally significant extent by repeated reflections between pigment particles. Very few pure white beams will pass right through the ink layer which might dilute the colour and cause the ink to appear pale.

In carrying the present invention into effect it is possible to use any transparent sheet such as glass, acrylic sheet or polycarbonate sheet. Glass is a useful cheap product and can be printed fairly easily. However, it is fragile and is not very easy to cut or shape. Further, adhesion between printing ink and glass is not always easy to achieve to form a product which is wear-resistant. Polycarbonate is an excellent and hard plastics material. It is, however, relatively expensive, and compatible printing ink systems are also expensive.

Currently, therefore, the preferred material for the sheet is acrylic material, that is to say a polyacrylate. (NOTE. I am guessing here, little bit of detail of exactly what is "acrylic" sheet is would be helpful!).

Acrylic sheet is preferred because of its cheapness and suitability, giving a virtually transparent material which can be formed into a sheet of uniform thickness (this is important When considering graded engraving) and because aerylate- compatible ink systems readily available.

Ink systems used therewith will normally comprise a pigment supported by a binder such as or including 2 butoxy ethanol with or without a gelling agent. In a preferred embodiment of ink of the invention and used in making the aforesaid sign the ink used is an acrylic based compatible ink comprising an acrylate-based binder containing pigment particles. The carrier may contain a gelling agent to prevent the settling out of pigment particles. In use, a quantity of the ink is first diluted with a desired quantity of a binder suitable for metallic pigment which is more likely to settle out of the binder than is non-metallic pigment. The metallic carrier is a2 butoxy ethyl acetate in a gel form. The ratio by volume of ink to carrier can vary. A low limit can be 1 volume of ink to 0.5 volumes of carrier (any less than this and there is little effect on the ink ) . This sort of ratio is useful in very light colours such as white or yellow. Usually, however, in practice at least one volume of carrier has to be added to one volume of a pale coloured ink in order to obtain the necessary light transmission, and the necessary colour illumination. Darker colours of all shades,but particularly dark blue and dark green, need a dilution of one part of basic ink to 12 or 15 parts of carrier. Dilution up to 1:20 parts is possible. However, in practice the effect caused by dilution of from 10 up to 20 parts carrier tends to produce a colour with a very high proportion of white light passing through the ink and therefore tends to be unacceptable except in some applications. Therefore, to obtain a light coloured blue or green it will be usual to use a green or blue ink of lesser intensity and use a dilution of only 10 or 12 parts by volume of carrier to 1 part of ink.

Figure 7a shows a typical sign (28) In the graph of figure 7 a, using, relating to non-diluted ink the intensity at about one third the length of a 300mm printed layer (29) has dropped to 12 which is about one third of intensity II. Between 12 and 13 the intensity drops slightly but not significantly. At the 13 position there is virtually no illumination of the ink from the light box (30) and it is clear that for roughly two thirds or more of the length of printed layer been 12 and 13 there is only a marginal illumination of the ink. This means that the portion of the ink between II and 12 glows brightly whilst the rest is, in very obvious contrast hardly illuminated.

In the graph shown in figure 2, however, it will be seen that the corresponding intensity 12 amounts to over 75% of the intensity of II and even at position 13, (that is to say the end of the printed layer) intensity has only dropped by 60% of the value of II. Although the drop in intensity from II to 13 may be considered significant in numerical terms, in terms of observers the fact that there is still a significant emission of light at the 13 intensity means that the drop in intensity from II to 13 perceived by the human eye is very small and the printed area therefore seems to be unifor ally illuminated.

The particular qualities of the ink and illuminated sign of the invention render it particularly suitable for use in combination with engraving. In the past, engraving has quite commonly been used in relation to such signs and with light passing down through the sheet a engraved channel has, naturally, reflected outwardly with a very attractive effect.

However, in relation to printed inks, the use of engraving has not been widespread in the particular way in which is envisaged by the present invention. In use with previous inks engraving at the edges or within inked areas has resulted in a slight increase of illumination but no significant increase as the light reflected from the engraving has contributed only slightly to the illumination of the ink because of the problems referred to aforesaid. With the present invention, however, the use of engraving leads to further advantages in the attractiveness and illumination of the sign. A typical sign (31) is shown in figure 6 and comprises a sheet of acrylic material (32) having a light box (33) . The sheet (32) has printed thereon two areas of ink (34) (35) which link is of the type described aforesaid.

In combination with such ink areas (34) and (35) the sheet (32) has been engraved as indicated at (36) (37) and (38) . The engraving can be carried out by a rotary cutter moved in relation to the sheet, or the sheet can be moved in relation to the cutter. The method is not important. When light travelling down the sheet (32) contacts the engraving, the naturally rough surface of the engraving (which is not polished) causes a diffusion of light which to the observer appears as a white line or outline depending on the shape or configuration of the engraving. This type of effect has been common with engraving in the past and is not novel. However, by placing the engraving at the edge of the ink areas (34) or even within the ink area as shown at (37) the diffuser effect of the engraved channel causes additional light to diffuse into the ink and increase the brightness of the ink area, for an ink area of particular shape, a closely surrounding border of engraving can not only form a white line emphasising the colour but can also cause diffusion of light into the ink which, because of its much more translucent nature, is more brightly illuminated at its edges giving a distinct attractive effect.

In accordance with a further feature of the invention and as shown in figure 6, it can be advantageous if the depth of the engraving is increased as the distance of the engraving from the light box is increased. At the position of engraving line (36) the light from the box (33) is relatively intense and only a relatively shallow groove or channel is necessary to form a bright observable light and to divert a significant amount of light into the ink area (34) . Midway down the sheet at the groove (37) the intensity of the light has fallen somewhat and therefore a slightly deeper groove (37) (or a deeper pair of grooves can be provided. Similarly at (38) where the intensity is reaching a lower value a deeper groove is formed which when observed by the eye is of generally the same or closely similar intensity to that of the groove (36) and which also diverts a greater quantity of light into the lower edge of ink area (35) so as to ensure that the emphasising effect is uniform.

If uniform engraving is used a good effect is obtained, but some of the engraving nearer to the light box can give a much brighter image than far engraving and therefore graduated engraving has its advantages in uniformity and in preventing the parts of the sign remote from the light box seeming to be dull.

The gradation from shallow engraving to deep engraving can be continuous throughout the sheet, but in practice it would be desirable for the movable engraving head to be programmed to cut deeper once a certain stage in its travel away from the light box (eventual) is reached. Of course, desirably the engraving head could be moved to cut in a constant plane and the sheet (32) , after printing, be laid beneath the cutting head in such a way as to have its plane not parallel to the plane of movement of the cutter but at a slight angle thereto so that as the cutter moves it cuts a deeper groove on one side of the sheet than on that side of the sheet which, in use, will have the light box attached.

The invention is not limited to the precise details of the foregoing and variations can be made thereto within the scope of the claims.

Claims

1. An ink, for example for an edge lit sign, wherein the pigment concentration is reduced below the conventional level.

2. An ink as claimed in claim 1, wherein the concentration of the pigment is reduced by addition of a carrier.

3. An ink as claimed in claim 2, wherein the carrier is the same type of carrier used in the conventional ink.

4. An ink as claimed in claims 2 or 3, wherein the carrier is a carrier conventionally used for supporting metallic particles in suspension in ink.

5. An ink as claimed in any preceding claim, wherein the action of the dilution of the carrier is such as to reduce the concentration of pigment particles within a given volume of ink whilst maintaining their uniform separation throughout the ink during application and drying of the ink.

6. An ink as claimed in any preceding claim wherein the dilution of the basic ink is by addition of 0.5 to 20 parts by volume of carrier per of ink.

7. An ink as claimed in any preceding claim and being a pale coloured ink diluted with from 0.5 to 5 parts by volume of carrier per part of ink.

8. An ink as claimed in any of claims 1 to 6 and being a dark ink diluted with from 9 to 20 parts of carrier per part of ink.

9. An ink as claimed in any preceding claim and including thinners not exceeding one part of thinners per ten parts by volume of ink carrier mixture.

10. An ink substantially as described with reference to the accompanying drawings.

11. A method of milking an edge lit sign including providing a sheet of transparent material, providing a light box at one edge of that material, and printing on one side of the sheet using an ink as claimed in any of claims 1 to 10.

12. A method as claimed in claim 12, wherein the degree of dilution of the ink is chosen such that the decrease in intensity of the observed light from the ink in a direction away from the light box is significantly reduced compared with conventional edge lit signs.

13. A method as claimed in claim 13, wherein the reduction intensity from the edge of the ink body adjacent the light box to its opposite side is less than 50%.

14. A method as claimed in claim 13, wherein the reduction is less than 25%.

15. A method as claimed in any of claims 12 to 14 wherein a reflecting surface is provided on an edge of the sheet remote from the light box.

16. A method as claimed in claim 15 wherein the reflecting surface is provided on the or all edges of the sheet remote from the light box.

17. A method as claimed in claim 16 wherein the surface is mirror reflective.

18. A method as claimed in claim 17 wherein the surface is diffuse reflective.

19. A method as claimed in claim 19, wherein the surface is white.

20. A method as claimed in any of claims 12 to 19, wherein the sheet is engraved.

21. A method as claimed in claim 20, wherein the engraving is carried out in register with an edge of a printed area or within a printed area.

22. A method as claimed in claim 20 or 21 wherein the depth of the engraving into the surface of the substrate is graduated so as to be shallower at a position adjacent the light box and deeper at a position remote from the light box.

23. A method as claimed in claim 22, wherein the graduation is a continuously variable graduation.

24. A method as claimed in any of claims 21 to 23 wherein engraving is carried out remote from or in register with but distant from the ink.

25. A method as claimed in claim 23, wherein the graduation is carried out in steps.

26. An edge lit sign made by a method as claimed in any of claims 12 to 25.

27. An edge illuminated sign comprising a sheet of transparent material and a light box on an edge thereof, a surface of the sheet having been printed with a diluted ink.

28. A sign as claimed in claim 27 wherein the ink has been diluted with a carrier to maintain pigment particles dispersed throughout the body of the ink.

29. A sign as claimed in claim 27 or 28 wherein the ink has been diluted sufficiently to ensure that the reduction in intensity across a printed area in a direction away from a light box is less than 50% from one side to the other.

30. A sign as claimed in claim 29 wherein the reduction is less than 25%.

31. A sign as claimed in any of claims 27 to 30 and being engraved.

32. A sign as claimed in claim 31 wherein the engraving is in register with an edge of an area of ink.

33. A sign as claimed in claim 31, wherein the engraving is uniformally spaced from the ink or is independent thereof.

34. A sign as claimed in any of claims 31 to 33 wherein the depth of engraving on the sheet varies in depth, being shallow adjacent the light box and deeper remote from the light box.

35. A sign as claimed in claim 34, wherein the graduation is in steps.

36. A sign as claimed in claim 34 wherein the depth of the engraving is smoothly graduated.

36. A sign as claimed in any of claims 27 to 35 wherein the degree of dilution and suspension is such that considered in a direction away from the light box a given length of pigment layer absorbs a percentage of incident light not significantly greater than its own length is a percentage of the full length of the pigment area.

37. A edge illuminated sign substantially as described with reference to the accompanying drawings.